A stereoscopic display usually presents an observer with images with parallax from individual right and left eye viewpoints. There are several techniques of providing the two eyes of the observer with the parallax images to produce a stereoscopic viewing experience. In a first technique, the observer utilizes a pair of shutter or 3-dimensional (“3D”) glasses which transmit or block light from the viewer's eyes in synchronization with alternating the left/right image display. In a second technique, right eye and left eye images are alternatively displayed and directed towards the respective eyes of the observer but without the use of 3D glasses. This second technique is referred to as autostereoscopic, and is advantageous for 3D viewing because there is no need for the observer to wear any type of specialized glasses. In some stereoscopic techniques, wavelength-selective glasses or polarized glasses must be worn by the viewer.
A liquid crystal display (LCD) is a sample-and-hold display device such that the image at any point or pixel of the display is stable until that pixel is updated at the next image refresh time, typically 1/60 of a second or faster. In such a sample and hold system, displaying different images, specifically displaying alternating left and right images for an autostereoscopic display, requires careful timing sequencing of the light sources so that, for example, the left eye image light source is not on during the display of data for the right eye and vice versa. Ensuring that the right and left light sources are on or off in synchronization with the image display is important to achieve a high quality autostereoscopic image.
Typically, when a liquid crystal display panel transitions from one image to the next, e.g., from a right eye image to a left eye image, different portions of the panel (i.e., different pixels of the panel) make the transition at slightly different times. For example, a top portion of the panel may make the transition first, followed by a middle or central portion of the panel, followed by a bottom portion of the panel. If the backlight is modulated between a left eye emitting beam and a right eye emitting beam uniformly over the entire output area of the backlight, crosstalk may occur over certain portions of the image. For example, a remnant of the left eye image may still be present on a portion of the display panel (e.g. on a bottom portion thereof) when the right eye beam of the backlight is turned on. Similarly, a portion of the right-eye image may appear on a portion of the display panel (e.g. on a top portion thereof) before the left eye beam of the backlight is turned off. This spatially-dependent time delay that characterizes the display panel's transition from one discrete image to the next gives rise to the desirability for a backlight whose output illumination can be controlled independently at different portions of its working area, so that the state of its output brightness (e.g. right eye beam on or off, and left eye beam on or off) can be synchronized with the state of the display panel both as a function of time and position on the working area of the display or backlight. Such a spatially addressable backlight, referred to as a scanning backlight, differs from conventional backlights in which all portions of the working area of the backlight are constrained to change from an “off” state to an “on” state, or vice verse, at the same time.
Scanning backlights for autostereoscopic displays are described in Patent Application Publication US 2008/0084512 (Brott et al.). Such backlights utilize a plurality of first light sources disposed on a first side of a light guide, and a plurality of second light sources disposed on an opposed second side of the light guide. In a non-scanning backlight, all of the first light sources would be illuminated (keeping the second light sources all “off”) while displaying a right eye image in the display panel so that the entire active or working area of the backlight is illuminated with light that propagates in a first direction corresponding to the observer's right eye. Similarly, all of the second light sources would be illuminated (keeping the first light sources all “off”) in a non-scanning backlight while displaying a left eye image so that the entire active or working area of the backlight is again illuminated, but with light that propagates in a second direction corresponding to the observer's left eye. In contrast to this, a scanning backlight may energize only one or some of the first light sources at a given time, and only one or some of the second light sources at a different time, so that only a limited portion (referred to as a segment) of the backlight, and thus only a limited portion of the display, emits right eye light or left eye light at any given moment. Selectively energizing different ones of the first light sources, and different ones of the second light sources, in a rapid sequence (in synchronization with the display) then allows all of the different segments of the backlight to be illuminated in a particular sequence or pattern to provide a scanning backlight.
The '512 Brott et al. publication describes achieving this type of scanning operation by use of a light guide construction that is “slatted”, e.g. as depicted in FIGS. 1 and 2. Briefly, FIG. 1 shows a schematic front view of a scanning backlight 30 for displaying alternating right and left images. This backlight is formed by cutting or otherwise making gaps 37 in a monolithic light guide to define distinct segments or slats 301, 302, 303, 304, 305, 306, 307, 308. The gaps 37, which may be air gaps, also separate at least a portion of each segment or slat thickness from an adjacent segment or slat. Each slat includes a first side or light input surface 31 adjacent to a plurality of first light sources 321, 322, 323, 324, 325, 326, 327, 328 or right eye image solid state light source, and an opposing second side or light input surface 33 adjacent to a plurality of second light sources 341, 342, 343, 344, 345, 346, 347, 348 or left eye image solid state light source.
The schematic side view of FIG. 2 depicts only three segments or slats, but is otherwise generally consistent with the embodiment of FIG. 1. A first surface 36 (subdivided by gaps 37 into first surfaces 361, 362, 363, and so forth) extends between the first side 31 and the second side 33, and a second surface 35 (subdivided by gaps 37 into second surfaces 351, 352, 353, and so forth) opposite the first surface 36 also extends between the first side 31 and the second side 33. The first surface 36 substantially re-directs (e.g. reflects, extracts, and the like) light and the second surface 35 substantially transmits light to a double-sided prism film and an LCD panel (not shown).
The gaps 37 of the slatted construction provide lateral confinement of light in the different slats of the light guide. For example, light from first light source 321 can propagate laterally within slat 301 between first light input surface 31 and second light input surface 33, and can be emitted from the second surface 351, of the slat 301, toward the prismatic film and LCD panel, ultimately to the right eye of the observer. But the gaps 37 allow little or no light from this source 321 to propagate laterally into any neighboring slats, such as slat 302.
Thus, each slat or segment includes a first light source transmitting light into a segment first side, a second light source transmitting light into a segment second side, and a light transmission surface and an opposing light re-directing surface which each extend between the segment first side and the segment second side. The plurality of segments are arranged substantially in parallel and with the first surfaces transmitting light in substantially the same direction to provide backlighting for a stereoscopic 3D liquid crystal display. These segments are selectively lit from one side of each segment and illuminating each segment sequentially down the display. The video or data signals may drive the LCD panel in synchronization with the sequential lighting of the segments down the display.